The invention relates to the field of DC to DC power conversion systems and provisions for making optimal use of the system described in conjunction both with the primary DC power sources available and the given loads power consumption demands.
The DC power converters which convert power from a primary DC power source into an output DC power draw defined by the load power consumption demands have become widely popular for feeding the electric and electronic circuits of varied devices. A great variety of DC-DC converter designs and circuitry have been invented and are used to address the variety of applications and requirements. Most common DC-DC converter designs were based on a primary power inductor or transformer, at least one switching transistor and an output filter capacitor. However, these prior art designs appear with large number of parts of substantial weight, volume and power losses, and with a limited power conversion density, i.e., the ratio of the number of watts per cubic inch or in regards to the overall cost. Attempts to increase the power conversion density by increasing the operational frequency have been ineffective. Primarily this is because proportional increases in power losses result in heat retention which undermine component reliability.
To overcome these disadvantages, a number of multiple converter topologies have been developed to improve power conversion density and overall power conversion performance. These are power sharing techniques which utilize multiple in-parallel arranged DC power converter units that are relatively small size. Each converter unit delivers only portions of the overall drawn power. Moreover, it is cost effective to design and manufacture standardized individual power converter units that combine into an array to feed a particular load, rather than to design and manufacture specific DC power converters to fit each application.
The power sharing DC-DC power conversion system includes at least one DC primary source, a multi-channel DC-DC power converter and a load. The multi-channel DC-DC power converters may be of any existing topology provided that it contains multiple internal switch-mode power conversion channels. The early prior art designs provide simultaneous operation of paralleled power conversion units. For multi-channel DC-DC power converter this means that each internal channel delivers its portion of power from a DC primary source to a load in a synchronously coincidental mode of operation (syn-phase, provided that all power conversion channels have a common operating frequency to trigger power-on cycles.
In a syn-phase mode of power conversion, all internal channels operate synchronously and simultaneously to each other. This synchronous operation creates large instantaneous power draws and large drops in the voltage of the primary power source. This instantaneous draw creates additional problems by introducing substantial input and output ripple. The ripple is caused by the simultaneous overlay of similar non-linear responses within corresponding circuits due to the non-linearity of any power conversion process.
Different multi channel converter configurations introduce different ripple constituents. In the case of parallel combined inputs and outputs, the input and output currents are summed within respective input and output circuits. The amplitude of the resultant primary source voltage drops increases proportionally to the N number of combined inputs. The resultant consumption and delivery currents have N times multiplied direct and ripple constituents as compared to the single power conversion channel.
In the case of series combined input and/or output power conversion channels circuits, the amplitude of the primary source voltage drop increases proportionally to the number of combined inputs. The resultant delivery voltage has N times multiplied direct and ripple constituents as compared to the same single power conversion channel.
Another disadvantage of the syn-phased power conversion is very slow response to changes in load. The time required responding to a change in load is limited to no less than one switching frequency period. In addition, the feedback circuit (used to control the power-on cycle interval) rate-of-response is severely limited to avoid feedback loops excited by ripple constituents.
Since all converters of the system have a common operating frequency, it was therefore determined reasonable to control the individual converters through staggered timing of their power-on cycles, i.e. in a poly-phase mode. In this way a power demand is also staggered over time eliminating the huge drops in primary power.
In poly-phase mode power, all channels operate with their power-on cycles time-staggered so, that there is a time displacement, xcex94tdspl, interval between the start-on points of the sequential cycles. Provided that all power conversion channels have the same operating frequency, the resultant summed input and output power draws show substantial improvement from the standpoint of primary power stress and output ripple constituents. Summing the time-staggered portions of converted power produces a filtering effect within the input and output circuits of the combined power conversion channels.
Since all the converters are driven out-of-phase in respect to each other, their non-linear responses are superimposed in a non-simultaneous and non-coincidental order. The result is a staggered inter-related compensation of overlapped portions of non-linear responses. This overlap decreases the non-linearity of the summed power draw.
It is therefore recognized inappropriate to increase the output power draw by increasing the number of parallel syn-phased power conversion channels since it produces proportional increase of input and output ripple constituents. However, increasing the number of poly-phased power conversion channels produces substantial decrease of input and output ripple constituents as compared with a single power conversion channel in the row.
However, the relative advantages of the prior art poly-phase mode power conversion approach do not provide completely satisfactory solutions to DC-DC power conversion.
There are many different applications requiring to deliver high quality DC power to a multiple loads from multiple low quality primary power sources. These varied applications make it desirable to have a modular power conversion system where small conversion units are combined in a single unit where their joint operation produces both a high quality and low loss power transfer from power source load demands.
It is evident that securing the high quality features of poly-phase power sharing DC-DC power conversion within the complex system configurations comprised of multiple primary power sources, DC-DC converters and loads may need more sophisticated control arrangement for operating the technical means. Thus, a better method and apparatus for power sharing techniques is needed.
The benefits of the proposed invention may be better disclosed through a comparative appraisal of the syn-phased versus poly-phased multi-channel power conversion systems.
The syn-phased power sharing DC-DC power conversion system, as shown at FIG. 1(a), includes at least one DC primary source 10, a multi-channel DC-DC power converter 12 and a load 14. The multi-channel DC-DC power converters 12 may be of any existing topology provided that it contains multiple switch-mode power conversion channels 16. Each internal channel 16 delivers its portion of power from DC primary source 10 to a load 14 in a synchronously coincidental (syn-phase) mode of operation. Syn-phase operation assumes all power conversion channels have common operating frequency for power-on cycles.
In a syn-phase mode of power conversion, all power conversion channels 16, as shown at FIG. 3(a), operate synchronously and simultaneously to each other. This coincidental operation creates large instantaneous power draws and large drops in the voltage of the primary power source with substantial input and output ripple. The ripple is caused by the simultaneous overlay of similar non-linear responses from all conversion channels. This is due to the non-linearity of any power conversion process.
In the case of parallel combined inputs and outputs, as shown at FIG. 2(a) and for boost power conversion channels with pulse width modulation control at FIG. 4(a) or for bridge-type resonant channels at FIG. 5(a), the input and output currents are summed within respective input and output circuits. The amplitude of the resultant primary source voltage drops increases proportionally to the number of combined inputs. The resultant consumption and delivery currents have N times multiplied direct and ripple constituents as compared with the single power conversion channel, as shown at FIG. 4(b,d) and FIG. 5(b).
In the case of series combined input and/or output power conversion channel circuits, as shown at FIG. 2(b,c,d) and for free running full-wave power conversion channels at FIG. 6(a), the amplitude of the primary source voltage drop increases proportionally to the number of combined inputs. The resultant delivery voltage has N times multiplied direct and ripple constituents as compared to the same single power conversion channel, as shown at FIG. 6(b).
In a poly-phase mode of power conversion all channels, as shown at FIG. 3(b), operate with their power-on cycles time-staggered so, that there is a xcex94tdspl interval between the start-on points of the sequential cycles. Provided that all power conversion channels have similar operating frequency, the resultant summed input and output power draws show substantial improvement from the standpoint of primary power stress and output ripple constituents. Summing the time-staggered portions of converted power produces a filtering effect within the input and output circuits of the combined power conversion channels, as shown at FIG. 4(c,e), 5(c) and 6(c).
Referring to FIG. 7(a,b,c,d), increasing the output power draw by increasing the number of parallel syn-phased power conversion channels produces a proportional increase of input and output ripple constituents. Conversely, increasing the number of poly-phased power conversion channels produces substantial decrease of input and output ripple constituents as compared with a single power conversion channel in the row.
The filtering efficiency achieved through poly-phasing the power conversion channels depends, though less substantially compared to the syn-phased method, on the interrelated symmetry, i.e. sameness of their internal electrical properties.
Referring to FIG. 8(a,c,e,g), the summed output current waveforms of four combined syn-phased power conversion channels depend on how well the core electric parameters match and on the main component values within the channels. A significant change of output current waveform shape is evident when a mismatch within any channel occurs. However, as shown in FIG. 8(b,d,f,h), the same mismatch in electrical parameters produces a substantially less significant impact to the shape of the summed output current waveforms when operated in a poly-phase mode.
Referring to FIG. 9(a,c,e,g,i), for eight combined in common syn-phased power conversion channels, the highest output ripple factor corresponds to a harmonic n=1 when a mismatch of any core parameters within any channel occurs.
Referring to FIG. 9(b,d,f,h,j), the same combined channels, operated in a poly-phased mode, produce a substantially reduced output ripple factor for n=mN (N=8 and m=1,2, . . . ) harmonic numbers and close to zero values of output ripple factor for nxe2x89xa0mN harmonic numbers depending on the degree of non-similarity of core electrical parameters within any channel.
Nevertheless, combining the power converting units into the complex configurations according to the existing needs may decline and undermine the advantages provided by the poly-phased power sharing approach to power conversion system configuring.
Exploring the of DC-DC power conversion system configuration shown on FIG. 1(b), wherein:
every DC-DC power converter 12 includes four internal power conversion channels 16 operated in a poly-phase mode,
every DC-DC power converter 12 includes one internal power conversion channel 16 affected by a random inner mismatch of interrelated time-displacement xcex94tdspl in accordance with condition pointed for FIG. 8(f),
every DC-DC power converter 12 outputs the resultant current Ioutxcexa3(t) as shown on FIG. 8(f), with ripple decreased as compared with the same of a single internal power conversion channel 16,
all three DC-DC power converters 12 are synchronously operated in a simultaneous, i.e. syn-phase mode,
therefore all three output resultant currents Ioutxcexa3(t) and their persistent residual ripples are coincidently superimposed within the load 14 producing the totalized output current xcexa3Ioutxcexa3(t), as shown on FIG. 8(j), with residual output ripple back multiplied and poly-phase mode advantages lost.
The same consideration is evidently valid for other complex DC-DC power conversion system configurations.
As shown on FIGS. 2(a,b,c,d), there are four different arrangements for combining in common the inputs and outputs of power conversion channels 16.
FIG. 2(a) is a block diagram of parallel-to-parallel power conversion channels 16 configured to deliver higher DC output current with the same DC output voltage that is delivered by a single unitary power conversion channel 16.
FIG. 2(b) is a block diagram of parallel-to-series power conversion channels 16 configured to deliver higher DC output voltages than can be delivered by a single power conversion channel 16.
FIG. 2(c) is a block diagram of series-to-series power conversion channels 16 configured to handle higher DC input voltages than can be handled by a single power conversion channel 16 and to deliver higher DC output voltages that can be delivered through a single power conversion channel 16.
FIG. 2(d) is a block diagram of series-to-parallel power conversion channels 16 configured to handle higher DC input voltages than can be handled by a single power converter and to deliver higher output power that can be delivered through a single power conversion channel 16.
The prior art poly-phased multi-channel DC-DC power conversion systems deliver an enormous increase of converted power draw compared with ordinary single channel converters. Nevertheless, it is not possible to increase the high quality power draw by simply increasing the number of power conversion channels added in parallel and included in the time-staggered chain.
The benefits of the poly-phase operation of multiple power conversion channels arise from the fact that the sequential power-on cycles are non-coincidental and also from the fact that the non-linear responses of the sequential power-on cycles overlap each other when being summed as portions of power draw.
It is well known from the science of system control that any technical object exhibits inertial properties when being forced to change from a stable state. The same concerns apply to power conversion channels. Activating the power-on cycle of power conversion is not short enough in time and the rise time interval between receiving the activating pulse from the control circuit and reaching the pre-selected rate-of-conversion should be taken into account. Thus, to secure a reliable non-coincidence of the sequential power-on cycles, the shortest interval of time between the sequential start-on points of power-on cycles should not be shorter then the longest interval of any channel within the power conversion system. In a contrary, the sequential power conversion cycles may casually coincide due to variations of individual rise time intervals and therefore exhibit a pseudo-syn-phase mode of operation while loosing all benefits of poly-phase mode of power conversion. It is evident that the number of power conversion channels included in a poly-phase chain should not exceed a certain number and this is the most significant limitation of the prior art poly-phase power conversion systems, which may be expressed as:
Nmax less than T/xcfx84max,
where Nmax is number of power conversion channels in a poly-phase chain,
T is the period of the switch-mode operation frequency,
xcfx84max is the longest rise time interval of any channel within the poly-phase chain.
The rise time interval xcfx84 also contributes to the limitation of general rate-of-response to changes in load and cannot be reduced beneath the value determined by physical bounds and the properties of existing art.
The purpose of this invention is to eliminate the limitations to increasing the converted power draw through increasing the number of power conversion channels included in a DC-DC power conversion system.
The further purpose of this invention is to improve the filtering efficiency of poly-phase mode DC-DC power conversion systems.
The further purpose of this invention is to eliminate the limitations for increasing the rate-of-response to changes in load within multi-channel DC-DC power conversion systems.
The quality of poly-phase power sharing in the DC-DC power conversion process, i.e. primary source stress, ripple contents and rate-of-response to a stepping load, depend exclusively on the extent to which the separate portions of drawn power compensate each others non-linear responses when being overlapped within the corresponding summing circuits.
The prior art poly-phase DC-DC power conversion methodologies are based on a single-chain of time-staggered power-on cycles of multiple power conversion channels. With prior art methodologies, smoothing the summed power draw relies on the overlay of said non-linearities. and do not provide the opportunity for their optimal regulation.
The improvement of the proposed invention is that the multiple power conversion channels are subdivided into a number of groups for bunching the in-group chained time-staggered power-on cycles of in-group arranged power conversion channels. The process provides a number of group based power-on cycle staggered chains within a power conversion system. Each group provides a cluster of time-staggered power-on cycles, i.e. power-on cluster.
The advantage of the proposed invention is that the time-staggered power-on cycles within a group may be adjusted for optimal compensation of non-linearities of the power segments processed by the in-group arranged power conversion channels, i.e. within a cluster. The result is a less non-linear power draw, i.e. power-on cluster draw.
The additional improvement of the invention is that the established groups, in their turn, are combined in common for the chained time staggering of the power-on clusters. This process allows the time-staggered power-on clusters to be adjusted for optimal compensation of non-linearity in the power-on cluster outputs, providing additional smoothing and improvement of overall power draw.
The additional advantage of the invention is that the number of power-on clusters, i.e. number of groups, number of power conversion channels, and amount of processed power may be increased as compared to prior art.
The invention further improves the DC to DC power conversion in that the chain-staggered power-on clusters each have a separate feedback loop. The locally distributed feedback loops provide better sensitivity and faster response time to changes in load and other random mismatches.
The further improvement of the invention is that power-on clusters may be combined into various configurations to adapt to the profile of the primary power source systems such as multi-source primary systems, and to the profile of the existing loads, such as a multi-load system.
The further advantage of the invention is that, due to the chain-staggered cluster approach, the high-linear power consumption may be secured for any configuration of primary power source and high-linear power delivery may be secured for any configuration of loads.
The clusterized poly-phase mode of power conversion may be used within the power supply systems shown at FIG. 1(a,b,c).
When, according to the prior art, the time-displacement exists only between the power-on cycles of unitary channels 16 within every modular converter 12 and no time-displacement exists between the power-on cycles of power converters 12 themselves, then the primary power sources and loads experience the syn-phase mode of superimposing the clusters of poly-phased channels 16 responses, as described above and with summed output current xcexa3Ioutxcexa3(t) shown on FIG. (8j) persisting multiplied residual ripple.
When, according to the prior art, the time-displacement exists only between the power-on cycles of modular converters 12 and no time-displacement exists between the power-on cycles of unitary channels 16 then both primary power sources and loads experience the poly-phased mode of superimposing the clusters of syn-phased channel 16 responses, and the totalized output current xcexa3Ioutxcexa3(t) may look quite similar to shown on FIG. 8(j) persisting large residual ripple.
When, according to the invention, the time-displacement exists both between the power-on cycles of the power channels 16 within every modular converter 12 and between the power-on clusters of modular converters 12, as shown on FIG. 8(i), then the primary power sources and loads all experience the poly-phased mode of power conversion and any non-linearity of overall power conversion draw may be compensated through a superimposition adjustment both within and between the power-on clusters, and therefore the summed output current xcexa3Ioutxcexa3(t) as is shown on FIG. 8(i) with the summed residual ripple decreased.
The quality properties of the prior art poly-phase power sharing conversion techniques are based on setting up constant values for time-displacement xcex94tdspl between the start-on points of the power-on cycles involved in a single-chain time-staggering, i.e.:
xcex94tdspl=T/N=const,
where T is the period of common operating frequency and N is the number of power-on cycles. Therefore, the process of superimposing the portions of converted power is rigid by nature and therefore the opportunities for improving the quality of the overall power draw is limited.
The further improvement of this invention is that variable values for interrelated time-displacement between the start-on points of the power-on cycles involved in a single-chain time staggering may be set up, i.e.:
0 less than xcex94tdsplxe2x89xa6T/N,
and variable values for interrelated time-displacement between the start-on points of power-on clusters may be set up, i.e.:
0 less than xcex94tdspl less than T/M,
where M is the number of clusters.
The above illustrates the further advantage of the clusterized poly-phase mode of power conversion in that a wide range of flexibility and power conversion efficiency is provided in adjusting for optimal compensation of non-linearity in the process of summing the portions of converted power.